How to Optimize Throughput in Wire Bonding Applications / Robert Ertel (ACS Motion Control Inc.)
Introduction
Wire bonding is the primary method of making electrical interconnections between integrated circuits and their
packaging. It is considered to be the most cost effective and flexible interconnect technology and is used to assemble
the vast majority of semiconductor packages. The wire bonding process is challenging from a controls standpoint – it
requires extremely high acceleration, short move and settle times, high accuracy, and high throughput. A powerful
motion control platform is required to achieve these stringent performance requirements. The following article
demonstrates why the ACS Motion Control solution is the most capable wire bonding platform.
Figure 1: Common “Ball Bonder” type wire bonding machine
About Wire Bonding
Wire bonding machines create bonds using (typically) gold wires which can be as small as 13um (0.5mil) in diameter.
Bonds are formed using a combination of heat, pressure, and ultrasonic energy to make a weld at each end of the
wire. Bonding machines are similar in appearance to sewing machines; there is a needle-like disposable tool called
the capillary through which the wire is fed and ultimately bonded to the semiconductor surface. There are four
general phases to creating a wire bond 1) bring weld bead to pad (semi-conductor surface) in position-control mode
2) detect contact between weld bead and pad and switch smoothly to force-control mode during formation of first
bond 3) once bond is complete, transition smoothly back to position-control mode and perform a coordinated XYZ
move to second bond location 4) transition smoothly to force-control mode for formation of second bond. Bonding
ACS Motion Control Ltd.
Ramat Gabriel Industrial Park, P.O. Box 5668
Migdal Ha’Emek 10500, ISRAEL
Phone: +972-4-6546440 Fax: +972-4-6546443
ACS Motion Control Inc.
6575 City West Parkway
Eden Prairie, MN 55344, USA
Phone: +763-559-7669 Fax: +763-559-0110
machines are three-axis systems comprised of a bond head (Z-axis) coupled to an XY stage. The bond head assembly
consists of a Z-axis voice coil with feedback resolution ranging from 0.1um to 2um powered by a high-bandwidth
amplifier (typically linear) for fast force response. Performance demands include fast response required for wire
clamping, and bonding accuracy better than 2um. The XY stage consists of linear three phase DC brushless motors or
voice coils with feedback resolution of 50-200nm driven by high power PWM amplifiers. XY performance demands
include high positioning accuracy of +/- 1um.
Technical Requirements
The goal for a wire bonding machine is to maximize throughput. Typical wire bonders can achieve 20 wires/sec which
requires very fast move and settle for all axes (XYZ), short profile times (few milliseconds), very high acceleration/jerk
(greater than 100g), minimal settling time with no overshoot, and prevention of vibrations at high frequencies. Other
requirements include coordinated XYZ motion, short overhead time for profile generation-to-motion, and high
volume/throughput real-time data transfer between host, controller, and drive. Requirements specific to the
bonding head include high current loop bandwidth (greater than 3kHz) for fast force response required for wire
clamping, high position loop bandwidth (greater than 200Hz) for fast settling, low impact force, fast contact
detection, suppressed force vibrations, and spring/gravity compensations.
ACS Solution
ACS utilizes an EtherCAT®-based, distributed control architecture and in doing so is able to create custom solutions
based on combinations of modular, scalable, standard product offerings. In a recent wire-bonding application, the
ACS control solution consisted of SPiiPlusSC + UDMlc + UDMba. The SPiiPlusSC (Soft Controller) is a state-of-the-art,
PC-based, zero-footprint controller with support for up to 64 fully coordinated axes and a 5kHz update rate. The
UDMlc is a lower-power, low-footprint, high-performance, quad-axis drive and is used to power the bonding head
axis. It also has the advantage of an extra (4th) axis which can be used for an additional non-demanding, typically
open-loop process (opening and closing a shutter, for example). The UDMba is a higher-power, high-performance,
dual-axis drive and powers the XY stage.
ACS Motion Control Ltd.
Ramat Gabriel Industrial Park, P.O. Box 5668
Migdal Ha’Emek 10500, ISRAEL
Phone: +972-4-6546440 Fax: +972-4-6546443
ACS Motion Control Inc.
6575 City West Parkway
Eden Prairie, MN 55344, USA
Phone: +763-559-7669 Fax: +763-559-0110
Solution Features
The SPiiPlusSC + UDMlc + UDMba solution has many standard and optional features which can be leveraged to meet
the demands of the wire bonding process. To begin with, the SPiiPlusSC offers the highest host-to-controller
communication throughput possible. Since the host application and SPiiPlusSC reside on the same PC, shared
memory and events are used for ultra-fast communication. Competing solutions rely on Ethernet communication for
this purpose, which creates a force-control bottleneck and limits performance capability. Another feature of the
SPiiPlusSC is a controller cycle time as low as 0.2msec resulting in shorter move times, reduced overhead, faster
controller response, and smoother profile generation and feed-forward compensations.
EtherCAT® is registered trademark and patented technology, licensed by Beckhoff Automation GmbH, Germany.
ACS has developed a number of special algorithms suitable for wire bonding, including “Soft Touch” force control,
“ServoBoost”, and “MotionBoost.” “Soft Touch” force control features a fast contact detection algorithm based on
several optional criteria; position error, drive command, or analog input (from force transducer). It also features nonlinear spring compensation, gravity compensation, and a damping mechanism to limit impact force and suppress
induced vibrations. For wire bonding, after collision is detected, force is applied based on a pre-defined timing
diagram after which the system switches back smoothly to position mode.
Figure 1: Force Mode timing diagram
The transitions from position mode to force mode and back are smooth and done within 50usec.
ACS Motion Control Ltd.
Ramat Gabriel Industrial Park, P.O. Box 5668
Migdal Ha’Emek 10500, ISRAEL
Phone: +972-4-6546440 Fax: +972-4-6546443
ACS Motion Control Inc.
6575 City West Parkway
Eden Prairie, MN 55344, USA
Phone: +763-559-7669 Fax: +763-559-0110
“ServoBoost” is a servo algorithm specially developed for highly demanding applications. With “ServoBoost” it is
possible to achieve maximal bandwidth and zero settling time to sub-micron resolution. “MotionBoost” is a new
motion profile technology developed in order to achieve minimal settling time and maximal dynamic performance.
Specifically, it generates specially designed motion profiles at the real-time servo update rate (20kHz) resulting in
very smooth and fast motion with durations as low as 100-500us. “MotionBoost” profile generation is superior to 2nd
and 3rd order motion profiles in that it results in reduced drive current during aggressive moves allowing for
increased throughput. “MotionBoost” also supports coordinated motion for up to three axes.
Figure 2: Regular Profile vs. MotionBoost
Yellow = regular profile
Green = MotionBoost profile
Red = position error (regular profile)
Blue = position error (MotionBoost)
Conclusion
Wire bonding is a challenging application, and with SPiiPlusSC + UDMlc + UDMba, ACS Motion Control provides the
highest performance solution available in the market today. The SPiiPlusSC controller is capable of maximal
throughput and cycle time with no footprint, and support for special algorithms necessary for handling such a highly
demanding application. UDMlc and UDMba drives feature low-footprint and high performance, and are ideal for wire
bonding. Many of the ACS products and features mentioned in this article are beneficial to applications beyond wire
bonding including automated IC programmers, PCB assembly, FPD inspection, wafer inspection, X-ray and CT
imaging, laser annealing, galvano mirror motion, and many others. In addition, ACS features dedicated and
experienced support personnel ready to assist with application challenges every step of the way; from machine
design to market launch.
For more information, please contact: [email protected]
ACS Motion Control Ltd.
Ramat Gabriel Industrial Park, P.O. Box 5668
Migdal Ha’Emek 10500, ISRAEL
Phone: +972-4-6546440 Fax: +972-4-6546443
ACS Motion Control Inc.
6575 City West Parkway
Eden Prairie, MN 55344, USA
Phone: +763-559-7669 Fax: +763-559-0110